1. Field of the Invention
This invention pertains to the field of manually-operated film scanning devices, and, in particular, to the illumination of a manually operated film scanner used as an input device to a television or like display.
2. Background Art
Manual image scanners are well known devices for inputting textual and pictorial information to a computer. U.S. Pat. No. 4,581,761 describes a typical ergonomically-designed housing including a linear sensor that is manually dragged by the hand of a human operator (hereinafter referred to as the "user") across the text or pictorial copy. A pressure sensitive switch on the bottom of the scanner turns the unit on when the user forces the scanner against the copy, and turns the unit off when the depression force is removed. Additional functions, such as variation of the enlargement or reduction ratio, may be engaged by keys on the top surface of the scanner. Notwithstanding such functionality, the scanner operates in but one scanning mode, that is, it inputs scanned data when the bottom switch is depressed and the linear sensor is swept across the copy. (U.S. Pat. No. 4,901,364 shows another example of a scanner capable of multi-functional operation, but only one scan capability.) If playback of the scan is needed, e.g., to evaluate the pictorial information, either the computer has to collect the linear scan data for a complete raster, or, as shown in U.S. Pat. No. 3,993,865, an intermediate store is provided for first collecting data from the manual scanner at a variable rate dependent on hand motion and then repetitively reading out the data at a constant rate for television viewing.
With each of the aforementioned scanners, it is necessary to provide some form of illumination. In U.S. Pat. No. 4,581,761, an optical system in the scanner includes an LED lamp array for irradiating light onto the paper being copied. In U.S. Pat. No. 3,993,865, the intermediate store also functions as a control unit, in particular providing an on/off brightness control. In U.S. Pat. No. 4,901,364, a hand-held character scanner includes user-programmable function keys and a light source comprising two LED devices. The turn-on time of the two LED devices is adjusted (presumably by the user) as a function of the reflective characteristics of the medium. In effect, the LED devices are driven on and off at a rapid repetition rate, thus forming a stroboscopic light source illuminating the medium surface bearing the characters.
Apart from the realm of hand-manipulated scanners, relatively larger desk-top scanners are available for high resolution scanning of slides or negatives in color or black-and white. An example is the 35 mm Rapid Film Scanner manufactured and sold by Eastman Kodak Company, Rochester, N.Y., which accommodates a functionally more complex illumination control than the aforementioned scanners. This scanner performs a color sequential high resolution area scan (1,312.times.1,024 pixel area) of color images in 18 seconds for input to a Macintosh.RTM. computer. Besides performing optical zooming panning, and cropping, the Rapid Film Scanner has a mode in which the image can be viewed either in monochrome or in color. The user selects the mode via a pull-down menu on the computer. Composing the image in color is difficult, however, because of the slow screen update rate due to the need to sequentially capture three color separations by rotating a filter wheel, and due to the color fringes which appear if the film image is moved while the separations are scanned. As a result, image composition is normally done in the monochrome mode.
Illumination in the Rapid Film Scanner is provided by a xenon flash lamp, and the amount of light is determined by the number of flashes per image scan. In turn, the number of flashes is determined from either an autobalance procedure or a manual balance mode. When the autobalance procedure is selected, the scanner computes the average brightness from the highest and lowest signal values from the last scan. The average brightness value is then used to adjust the number of flashes for the next succeeding scan. To adjust the illumination manually, the user pulls down the computer menu, and selects the manual balance mode. Then a computer mouse is used to move screen-based "sliders" which vary either the overall brightness or the brightness separately in the red, green and blue channels. Alternatively, the exact number of light flashes can be entered into the keyboard. To then examine the adjusted image in color, the user must pull down the computer menu, and select the color mode. Once the color image is captured, the user must pull down the menu again, in order to return to the monochrome mode, and compose the next image. This means, particularly for manual adjustment of the illumination, that the user must continuously switch from handling the scanner to handling the computer pointer, typically by manipulating a mouse. This is a tolerable situation for user scanning of only a few images, as is typically the case in applications where such a scanner is used. It is less acceptable in the case where real-time interactive image input is desired.